Jellyfish Lake, Palau
Mastigias sp. jellyfish @ Jellyfish Lake, Palau
Evolution is cool. A long time ago, this body of water was sealed off from the ocean, its inhabitants left to evolve by themselves. Having no predators except for anemones along the lake's perimeter, the jellyfish in the lake (virtually) lost their ability to sting. They developed their symbiosis with photosynthetic algae, and now live by basking in the sunlight. During the day, the school of hundreds of thousands (if not millions) of jellyfish migrate around the lake, following the sun. They bob up to the surface and expose themselves for nourishment.